Date of Award

1993

Degree Type

Thesis

Degree Name

Bachelor of Applied Sciences Honours

Faculty

Faculty of Science and Technology

First Advisor

Dr Pierre Horwitz

Abstract

The effect of seasonal or permanent inundation on the processing of leaf litter from two competing emergent macrophytes Baumea articulata and Typha orientalis was examined at Lake Jandabup, a seasonal wetland on the Swan Coastal Plain. The loss of organic matter from leaf packs was used to quantify leaf litter processing. The contributions made by microorganisms and macroinvertebrates in processing were also assessed. Leaf packs exposed to seasonal inundation (defined as those areas exposed to alternate wetting and drying) had significantly higher losses of organic matter after six months than those permanently inundated for the same period. The presence of stratified water column in the permanently inundated sites in summer, resulting in reduced oxygen levels at the bottom or the water column appears to be the driving force behind the low amounts of organic matter loss from leaf packs in this environment. These results are supported by the presence of peaty soils in the permanently inundated sites and not in those seasonally inundated, indicating that this pattern of leaf litter processing has been occurring for some time. The reflooding of seasonally inundated sites resulted in these leaf packs having the highest microbial biomass and therefore become a preferred food source for invertebrates. Losses of organic matter from leaf packs also highlighted the difference in the amounts of organic matter loss between the two species, with Baumea losing significantly more. The classification into groups of macroinvertebrates found in leaf packs using TWINSPAN resulted in a separation of the permanently inundated sites into distinct invertebrate communities, with no preference for Haumea or typha leaf packs found in established vegetation communities. The resulting differences in functioal feeding group representation between vegetation communities may in part be responsible for differences in the amounts of leaf litter processing. The results from this study indicate that changes to the current seasonal wet/dry hydrological regime experienced by the littoral community at Lake Jandabup will alter the proportions of organic matter available for processing within the wetland

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